1. Field of the Invention
This invention relates generally to an apparatus for performing in-service measurements of the quality of a video transmission or storage system. The video may include moving images as well as still images. The video transmission or storage systems may include, but are not limited to, digital video encoders and decoders, video storage/retrieval systems, analog transmission circuits, and digital transmission circuits. The apparatus measures in-service video quality even when the input and output ends of the video transmission system are spatially separated and the input video is not known a priori by the apparatus. Rather than injecting known video signals into the video transmission system and making measurements on these, the apparatus attaches nonintrusively to the input and output ends and makes measurements on the actual program material being sent over the video transmission system. The apparatus makes measurements using actual program material by extracting features indicative of video quality from the input and output ends, communicating these extracted features over an ancillary data channel, and then calculating quality parameters based on the extracted features. The apparatus has the ability to make video quality measurements using ancillary data channels of arbitrary and possibly dynamic bandwidths. In general, the apparatus makes coarser quality measurements, i.e., coarser in the sense that extracted features come from larger spatial-temporal (S-T) regions, when smaller capacity ancillary data channels are available, and finer quality measurements when larger capacity ancillary data channels are available. This makes the apparatus very versatile in that many different types of ancillary data channels may be used by the apparatus. Some examples of ancillary data channels that may be used by the apparatus include modem connections over the Public Switched Telephone Network (PSTN), Internet connections, Local Area Network (LAN) connections, Wide Area Network (WAN) connections, satellite connections, mobile telephone connections, ancillary data channels in modem digital video transmission systems, and data sent over the vertical interval in the analog NTSC video standard.
2. Description of Prior Art
Devices for measuring the video quality of analog video transmission systems have been available for many years. All of these devices utilize standard test patterns or signals (such as a color bar) that are injected into the video system by the measurement apparatus. In these cases, since the measurement apparatus has perfect knowledge of the input test signal, video quality measurements are made by examining distortions in the resultant output from the video transmission system. Further, in-service measurements are made by injecting test signals into only the non-visible portion of the video signal (e.g., the vertical interval in the NTSC video standard) while the visible portion carries the normal program material observed by the viewer.
With the advent of new digital video systems that utilize compression to achieve a savings in transmission or storage bandwidth, the quality of the received output video may be highly dependent upon the inherent spatial and temporal information content of the input video. Thus, it no longer makes sense to make quality measurements using video signals injected by an apparatus, since the resultant quality of these injected signals may not relate at all to the resultant quality of actual program material. Thus, a new method is required to make in-service video quality measurements on actual program material.
Many systems have been developed in recent years to make video quality measurements by comparing input and output video images of actual program material. One such common system computes the mean square error between the input video and output video stream. However, most of these systems require complete knowledge of each and every pixel in the input and output video to work properly, and hence these systems are only practical for the following special cases:
(1) Out-of-service testing when the input video is known perfectly a priori by the apparatus.
(2) In-service testing when the input and output ends are either in the same geographic location or when a high bandwidth ancillary data channel is available to transmit a perfect copy of the input video to the output video end.
It should be noted that in the second case, the ancillary data channel bandwidth required to transmit a perfect copy of the input video is on the order of 270 Mbits/sec for broadcast applications. This sort of extra bandwidth is rarely available between the input and output ends of most common video transmission channels.
An in-service video quality measurement system that uses actual program material and that does not require perfect copies of the input and output video has been developed. This system was first presented in U.S. Pat. No. 5,446,492 issued Aug. 29, 1995, and then updated in U.S. Pat. No. 5,596,364 issued Jan. 21, 1997. However, no mechanism is identified in the apparatus of these patents that enables the apparatus to automatically adapt to increasing ancillary data channel bandwidth with the intent of producing finer, and hence more accurate, measurements of video quality.
It is accordingly an object of the present invention to provide an improved method and system for performing in-service measurements of the quality of a video transmission or storage system. Here, the video transmission or storage systems may include, but are not limited to, digital video encoders and decoders, video storage/retrieval systems, analog transmission circuits, and digital transmission circuits. The term in-service means that the input and output ends of the video transmission or storage system may be spatially separated, and that the input video to the video transmission or storage system is not known a priori by the video quality measurement system.
Another object of this invention is to provide a method of adjusting the coarseness of the in-service video quality measurements based on the amount of bandwidth that is available in an ancillary data channel, with finer measurements being made for increased ancillary data channel bandwidths.